U.S. Pat. Nos. 5,895,854 and 6,308,758 and copending U.S. patent application Ser. No. 09/584,230 disclose a vehicle wheel that is provided with a pneumatic (rubber) tire having at least at one predetermined location a rubber mixture that is permeated with magnetizable particles that have been magnetized. As stated in that patent, the tire disclosed therein can be used in a slip regulation system. Preferably, the magnetized locations are located in one or more annular bands in the sidewall of the tire, i.e., in the longitudinal or peripheral direction, and have successive zones of different magnetization in one or more rows disposed at different radii along the peripheral direction of the tire. One expressly stated object of the '854 patent was to provide a vehicle wheel having a pneumatic (rubber) tire, with the aid of which the information required for operating a modem vehicle, e.g. wheel rotational speed for ABS (Anti-lock Brake system) and/or longitudinal forces (torsional forces) that act upon the tire for regulating slipping, can be made available.
According to that patent, the generated magnetization and the spatial magnetization differences could be detected with magnetic field sensors and can serve as SWT sensor input signals (sidewall torsion sensor input signals) for slip regulating systems, especially also for SWT systems (sidewall torsion measuring systems). As further stated in that patent, it was previously thought that in order to be able to detect a change of the time span between the passes of the two marks (in one row for ABS or in two rows for SWT) as precisely as possible, it was desired that the magnetization in the peripheral direction be effected as quadrilaterally as possible, i.e. that the magnetization should be substantially homogeneous within a cohesive region (code bars), and above all at the boundaries of this region should change with as great a gradient as possible. In contrast, it was stated that for the conventional ABS systems that detected the wheel rotations, it was sufficient if the magnetization in the peripheral direction of the tire be effected in a sinusoidal manner.
Thus, a primary function of the SWT system using the SWT sensor has always been to measure the torsional deformation in the tangential direction of the tire and use that torsional deformation to calculate the applied driving or braking torque. Copending U.S. patent application Ser. No. 09/584,230, provide a system and method for decoupling the lateral and tangential forces acting on the tire to allow the SWT sensor to be used to effectively measure longitudinal torque, and also to predict the lateral force and other forces and torques acting on the tire using the SWT sensors.
Because of the unique construction of each tire, e.g., locations of various splices, minute differences in material thicknesses, each tire has its own magnetic field sidewall “fingerprint” or “signature” that can be detected by the SWT magnetic sensors. These signatures may be, but are not necessarily, unique for each tire. FIG. 1 shows one such tire signature showing, for one revolution of the tire, magnetic field plotted against pole number around the circumference of the magnetized region of the tire. FIG. 1 indicates generally the physical characteristic of the tire responsible for some of the more dramatic features of that particular signature: the builder splice, the sidewall splice, and the stock preparation splice. This signature repeats every revolution of the tire. In the applications of the SWT systems mentioned above, including the systems and methods in patent application Ser. No. 09/584,230, the individual features of this signature were essentially ignored as part of determining the forces acting on the tire.